1. Field of the Invention
The present invention generally relates to a hydraulic breaker for breaking an object by means of a chisel which is struck by a piston driven by hydraulic pressure and nitrogen gas.
2. Description of the Prior Art
In a known hydraulic circuit of a hydraulic breaker, oil is supplied from an oil tank 10 through a pump 11 and an operating valve 12 to the hydraulic breaker 15, as shown in FIG. 2. Then, the oil purged from the hydraulic breaker 15 is returned to the oil tank 10 through a filter 13 and an oil cooler 14. Thus, the oil is circulated from the oil tank 10 through the pump 11, the operating valve 12, the hydraulic breaker 15, the filter 13 and the oil cooler 14 to the oil tank 10.
The hydraulic breakers referred to above include direct-acting hydraulic breakers in which the piston is directly driven by the oil pressure, gas-type hydraulic breakers or spring-type hydraulic breakers in which the piston is driven to strike the chisel by the reaction force of nitrogen gas or a spring compressed within a cylinder. In any of the aforementioned types of hydraulic breakers, not only is an accumulator necessary for supplying oil to a piping at the oil supplying side, but also an accumulator is necessary for preventing pulsation in a piping at the oil discharging side. For example, in the gas-type hydraulic breaker shown in FIG. 1(a), a piston 1 is lowered under the reaction force of compressed nitrogen gas, with without requiring high pressure oil. Accordingly, the oil pressure is stored by an accumulator 3 installed in a high pressure circuit 2. On the other hand, in a low pressure circuit 4, when the piston 1 is lowered, an upper chamber 5 of the piston communicates with a lower chamber 6 of the piston so that low pressure oil is circulated to close the passage to the low pressure circuit 4. When the piston is raised as shown in FIG. 1(b), since the passage is opened to allow the flow of a large quantity of oil, the oil pressure is stored in an accumulator 7 so as to control the pulsation, thereby preventing the breakage of the filter or the oil cooler resulting from the increase in surge pressure.
As mentioned above, although the prior art hydraulic breaker needs accumulators in both the high pressure circuit and the low pressure circuit, the accumulators are apt to malfunction because of the leakage of gas, and therefore regular inspection, exchange and repair of accumulators are disadvantageously required,. At the same time, the prior art hydraulic breaker has a complicated structure, attributing to a high manufacturing cost.
Moreover, in the gas type hydraulic breaker as shown in FIG. 1, the piston 1 is raised by the high pressure oil, and the lowering of the piston 1 is carried out by the utilization of the reaction force of nitrogen gas, and therefore, the striking force of the piston can not be strong enough even though there is an accumulator at the high pressure circuit to raise the oil pressure or increase the quantity of oil.